EC2 has two types of instances:
- Fixed Performance instances (e.g. M3) - These give consistent performance instances
- Burstable Performance instances (e.g. T2) - They provide a fixed performance when the workload is normal, and when there is a spike in the workload it has the ability to increase the CPU performance (or burst).
So, CPU Credit will regulate the amount CPU burst of an instance. These credits can be used to increase CPU performance during the Burst period. For example, if you are using your instance at 100% for 5 mins, you are spending 5 credit(5 * 1.0). And, if you are using at 50% for 5 mins, then it would be (5 * 0.5).
CPU Credit Balance - the amount of CPU Credit balance available in your AWS account at a given time.
When you create you will get initial CPU Credits, also every hour of usage you will get a certain amount of CPU credit according to the instance you have launched. So, if you do not burst your instance, then your credits will be saved. But once you run of credits, you cannot burst and the CPU will run in the fixed performance.